This invention relates to differential amplifying systems and, more particularly, to a system for amplifying a differential component of a composite signal and rejecting the common mode component of the composite signal.
Many differential amplifying configurations have been proposed to amplify the differential component of a weak signal while rejecting the common mode component. Precise impedance relationships must be established in many of the differential amplifying systems known to the prior art. These impedance relationships must be maintained to assure effective operation. Specifically, the impedance difference created by unequal lead lengths to the composite signal source is often enough to disturb the precise impedance relationship so that the common mode component is not fully rejected.
Also, the gain of the differential amplifying systems known to the prior art is not adjustable without additional adjustment of the established impedance relationships. Moreover, the magnitude of the common mode component must be kept smaller than the supply voltage to the differential amplifiers to assure the complete rejection of the common mode component.